1. Field of the Invention
The present invention relates to an apparatus and a method for measuring voltage such as to monitor voltage of a power source.
2. Description of the Related Art
A fuel cell stack mounted in a fuel cell vehicle is a stack of a great number of cells formed by, for example, a solid polyelectrolyte membrane placed between an anode electrode and a cathode electrode which are further sandwiched between a pair of separators. This kind of fuel cell stack has a voltage monitor for monitoring voltage of each cell to detect malfunction of the cell as soon as possible. For example, in a fuel cell stack disclosed in JP 11-339828A (Paragraph 0009), a detecting terminal is provided on each of separators of each cell, and plural connecting terminals are provided on a connector and connected to these detecting terminals, so that the voltage can be monitored.
Meanwhile, in a fuel cell stack, a great number of cells are connected in series to obtain high voltage since cell voltage of each cell is as low as about 1 V (volt). Accordingly, when malfunction causing electromotive force to be reduced occurs in one of the cells, the malfunction of the cell may spread to the other normal cells and causes total power supply obtained from the fuel cell stack to be low. Therefore, it is required to measure cell voltage of each cell correctly.
However, in a fuel cell stack, 0 volt may be output as cell voltage when power is not generated even though no malfunction occurs. Therefore, there is a problem that it is impossible to determine whether the detected output voltage is actual cell voltage or caused by faulty electrical continuity between detecting terminals and connecting terminals of a connector.